JP5856279B2 - Position sensor - Google Patents

Description

The present invention operates in a non-contact manner allowing the relative displacement and / or relative position of two opposing objects to be measured by measuring the magnetic field strength of the electromagnetic field emitted by the transmit coil and detected using the receive coil. It relates to a distance sensor.
Specifically, the present invention relates to a position sensor having two coils, of which a first coil (transmitting coil) is supplied with a specific frequency so that it emits a certain electromagnetic field, and the electromagnetic field Is received or detected by the second coil (receiving coil).

Sensors that measure the relative displacement of two objects are generally known.
There are different measurement principles, each principle having certain advantages and disadvantages.
The best resolution must be selected depending on requirements such as accuracy, resolution, temperature dependence, measurement speed, long-term stability, allowable power loss, and dominant environmental conditions.
In this regard, there is a very high demand in position and displacement measurement in the precision optical element field.
This involves accuracy in the nanometer and sub-nanometer range, and two application areas are particularly important.

Micropositioning in semiconductor manufacturing, and relative position adjustment of split mirrors in a reflective telescope for astronomical observation.
In the past several different principles have been used.

Very accurate measurements can be made using optical sensors. The capacitive sensor is also very accurate.
One example is described in FR2844848A1.
The main drawback of both principles is that the measurement depends on the effects of moisture and dust.
They are also unsuitable for use with reflective telescopes in principle.
Although path sensors that operate according to the eddy current loss principle are insensitive to water and dust, the temperature dependence of the measurement can only compensate for the required accuracy at a very high cost.

French unexamined application FR2907211A1 solves the above-mentioned problems by arranging a coil arrangement of a conductive measurement object mounted on an opposing mirror segment.
In this case, the change in inductance caused by the measurement object as a function of the position relative to the individual coils of the array is evaluated.
Using this arrangement, measurements can be made in three axes.
The disadvantage of this arrangement is a relatively large structure, and thus a great dependence on mechanical deformations caused, for example, by temperature changes.
The role of the temperature-dependent conductivity of the coil and measurement object cannot be ignored.

  Therefore, the transformer principle with primary and secondary coils (transmit and receive coils) remains the only possibility.

For this purpose, US Pat. No. 4,816,759 describes an arrangement having two oscillators feeding power to two transmitter coils connected in series and two receiver coils each comprising a parallel capacitor and constituting an oscillation circuit. .
One of the two transmit coils is mounted on the surface of the mirror element.
Corresponding receive coils are arranged on the faces of the opposing mirror elements.
The second transmit-receive pair is offset at the same height along the two faces of the mirror element and placed in the reverse transmit-receive direction.
The displacement between transmitter and receiver is evaluated by phase measurement.
The zero passage of the phase position of the measurement signal here results in a coincidence of the parallel planes of the mirror segments.
This principle is inherently suitable for adjusting the parallelism of segments, but does not provide other additional information such as angles and distances between segments.

WO 2007/006910 describes the transformer principle using two primary coils (transmitting coils) connected in series and two secondary coils (receiving coils) facing each other.
The coils are arranged as flat (planar) coils, and each of the transmission coil and the reception coil is disposed adjacent to and parallel to each other.
AC signals are supplied to the transmission coils in opposite phases.
Using this principle, an accurate zero point record can be obtained by measuring the difference between the two received voltages.
At the same time, the distance between the two mirror elements can be measured by adding the two received voltages.
The distance dependence in the measurement of the parallelism of the mirror segments to each other can be eliminated by forming a ratio between the differential voltage and the summed voltage.
However, the angle dependence cannot be excluded.

  A further disadvantage is the large surface required for the coil. This is because, for example, mechanical deformation due to thermal expansion plays a role that cannot be ignored.

  The problem underlying the present invention is to avoid as many of the disadvantages previously encountered in the prior art as possible.

The present invention has two coils, a specific frequency is supplied to radiate a constant electromagnetic field to the first coil (transmitting coil), and this electromagnetic field is received by the second coil (receiving coil), Alternatively, a position sensor to be detected is included.
It has two coils and the first coil (transmitting coil) is supplied with a specific frequency so that it emits a constant electromagnetic field, and this electromagnetic field is received by the second coil (receiving coil). Or a position sensor to be detected.

  The principle underlying the present invention is as follows.

The two coils form a transformer, with one coil acting as a primary coil (transmitting coil) and the second coil acting as a secondary coil (receiving coil).
The coupling relationship between the coils changes when the relative position of the two coils changes.
The two coils are arranged so that they are perpendicular to each other, and the axis of the transmitting coil is arranged parallel to the plane of the receiving coil.

According to the description of FIG. 2, the transmission coil 1 is supplied with a high-frequency AC voltage having a constant amplitude.
A voltage of the same frequency is induced in the receiving coil 3 by an alternating electromagnetic field.
The voltage level depends on the coil coupling state, where the coil coupling state depends on the relative position of the coils to each other.

In a special arrangement (FIG. 6), the position of the object to be measured is determined using several coils.
The two transmission coils 1a and 1b are supplied with an AC voltage having the same or different frequency and the same or different, but with a constant amplitude.
Equally supplied coils can be connected in parallel or in series.
A voltage is induced in the reception coil 3 facing the transmission coil 1b.
A voltage is also induced in the receiving coils 5 and 6.
These receiving coils 5 and 6 are aligned in parallel with each other and are arranged to face the transmitting coil 1a.
Measurements can be performed in the z direction using the receive coil 3 and in the x and y directions using the receive coils 5, 6.
That is, the displacement of the receiving coils 5 and 6 parallel to the transmitting coil 1a in the x direction is proportional to the difference between the signals from E5 and E6 (E5 to E6).
On the other hand, the change in the distance between the receiving coils 5 and 6 with respect to the transmitting coil 1a in the y direction is proportional to the sum of signals from E5 and E6 (E5 + E6).

The transmission coils 1a and 1b are driven using a known oscillation circuit.
It is beneficial to supplement the coils with parallel capacitors and drive them to resonance because the sensitivity is particularly high and the required current is low.

The measurement arrangement according to the invention is in particular characterized by a very high sensitivity (with respect to measurement) such that a very high resolution is achieved.
In a typical arrangement with a measurement range of 500 μm, sub-nanometer range resolution can be obtained.
The required coil dimensions are relatively small.

In order to reduce EMC radiation, the transmitter coils 1a, 1b can be operated in antiphase.
Since the electromagnetic field is attenuated at a remote location, the interference effect is also reduced at the remote location.
In order to reduce the sensitivity of the receiving coil 3 to interference, the ratio of the signal from E3 and the sum signal from E5, E6, ie E3 / (E5 + E6) is used for the measurement.
Therefore, the influence of interference that acts on the receiving coils 3, 5, 6 in the same manner is largely eliminated (for example, EMC failure or particularly temperature effect).
In order to achieve the same effect, it is required that the receiving coils 3, 5, 6 are arranged sufficiently close to each other.
In the same way, compensation for interference effects is achieved with respect to the measurement of displacement in the x-direction by forming a ratio between the difference between 5 and 6 and the sum ((E5-E6) / (E5 + E6)). The

  The invention can best be explained using specific examples.

The position is detected in three directions, that is, a change in the distance of the sensor plate B with respect to the sensor unit A (y direction), or a displacement of the sensor plate B with respect to the sensor unit A (x direction) or a displacement in the z direction is detected. Any suitable measurement mechanism can be used.
Depending on the relative arrangement of the coils, three independent signals for the directions x, y and z can be generated.
It is beneficial to place the coils in close proximity to each other to obtain a compact structure and to achieve the same effect required for compensation.
The coil can be formed, for example, as a flat (planar) coil on a common circuit board.
This makes manufacturing particularly simple and cost-effective, but the temperature stability and long-term stability are not particularly high.
An electronic circuit for driving and evaluating the coil can also be placed on the circuit board so that the placement is compact and beneficial.
Another embodiment is characterized by the fact that the coil is manufactured by a known method as a flat (planar) coil on a ceramic substrate.

It is particularly beneficial if the coil is manufactured on a ceramic multilayer substrate and the coil is located inside the sandwich structure.
At this time, the coil is completely sealed from the surroundings by hermetic encapsulation that occurs in the ceramic multilayer manufacturing process.
As a result, a coil having a structure with particularly long-term stability and excellent temperature stability can be obtained.
Thus, the manufactured coil is characterized by excellent (hermetically sealed) environmental and long-term stability.
This is a real advantage if the high resolution of the measurement assembly can be exploited.
It is particularly beneficial if the coil is designed as a coil having a rectangular surface rather than as a circular coil.
At this time, the resulting electromagnetic field in the coil surface is almost constant.
For example, during the evaluation of measurements in the y direction, the resulting measured value depends only on the decrease in the electromagnetic field strength in the y direction (roughly inversely proportional to the distance) and does not depend on the coil shape, so Give the desired effect.

The measurement assembly described above can be used at any location where a very accurate distance or position is measured.
The second described assembly is particularly suitable for measurements in all three spatial coordinates, particularly where high resolution and stability requirements are a priority.

  An example of this is as follows.

Micropositioning in semiconductor manufacturing (wafer stage): In this case, the wafer must be very accurately aligned with the exposure axis during semiconductor manufacturing.
As the structure width used in current semiconductor processes becomes increasingly smaller, accurate positioning is required for quality assurance.
Further exposure systems that work with EUV radiation require positioning accuracy in the picometer range.
This is possible with this measurement arrangement.

Positioning the split mirror in a reflective telescope: Modern reflective telescopes no longer consist of one large mirror, but consist of a number of individual mirrors arranged in a honeycomb.
The individual mirrors must be precisely aligned with each other so that the light is accurately focused in focus during astronomical observation.
Due to the large distances observed with these telescopes, the positioning accuracy of the individual mirrors is a few nanometers.
As a result, the mirror must be accurately aligned in all three spatial directions to achieve focus at the focus.

Here, there are different possibilities to advantageously configure and change the instructions of the present invention.
For this purpose, reference is made, on the one hand, to the description of several claims subordinate to claim 1, and on the other hand to the following description of preferred embodiments of the invention with reference to the drawings.
Along with the description of the preferred embodiment of the present invention with reference to the drawings, a variant of the teaching (Lehre) and the preferred embodiment are also generally described.

1 is a schematic view of an assembly arrangement known from the prior art. 1 is a schematic diagram of an embodiment of the present invention. 1 is a schematic diagram of an embodiment of the present invention. FIG. 3 is a schematic view of an embodiment of the present invention as a combination of the assembly of FIGS. 1 and 2. 1 is a schematic diagram of an embodiment of the present invention. FIG. 3 is a schematic diagram of an embodiment of the present invention extended to three measurement axes. 1 is a schematic diagram of an embodiment of the present invention. 1 is a schematic diagram of an embodiment of the present invention.

According to the description of FIG. 1, a specific frequency (S) of constant amplitude is supplied to a suitable rectangular coil (1) so as to emit a constant electromagnetic field.
This is received by the second receiving coil (2) arranged so as to be the same axis as the axis of the transmitting coil.
The reception voltage (E2) directly depends on the distance between the transmission coil (1) and the reception coil (2), that is, the distance in the y direction.

This voltage is nonlinearly dependent on the distance and decreases continuously with increasing distance.
The characteristic must be linearized by calculation or circuit so that the distance between the coils can be measured in reverse phase.

FIG. 2 shows an embodiment of the arrangement according to the invention.
The complete rectangular coil (1) is supplied with a specific frequency (S) of constant amplitude so that it radiates a constant electromagnetic field.
This is received by a second receiving coil (3) whose axis is located 90 ° perpendicular (z) to the axis of the transmitting coil (1).

When the receiving coil (3) is located at the center with respect to the rectangular coil (1), the generated magnetic field lines do not intersect the receiving coil (3), so that no induced voltage (E3) is generated at the coil end.
Using an asymmetrically acting magnetic field creates a voltage at the coil ends that changes linearly over a specific range on either side of the center position with a parallel positioning displacement (direction z), where When passing through the center position, the phase position is rotated by 180 ° with respect to the transmission signal.
In this way, a simple sensor can be realized, which can be used to measure the parallel displacement of the two coils relative to each other and the achievable measurement path is somewhat larger than the coil diameter of the transmitting coil. small.
As already explained, the induced reception voltage is linear in the central region and gradually increases in non-linearity towards the edge of the region.
At this time, the characteristic of the gradient on the measurement path depends on the basic distance of the coil.

According to the description of FIG. 3, a suitable rectangular coil (1) is supplied with a specific frequency of constant amplitude so that it radiates a constant electromagnetic field (S).
This is received by a second coil (4) whose axis is positioned at 90 ° in the horizontal direction (x) with respect to the axis of the transmission coil (1).

Similarly to FIG. 2, when the second coil (4) is located at the center with respect to the rectangular coil (1), the induced voltage (E4) is not generated at the coil end.
Using an asymmetrically acting magnetic field creates a voltage at the coil ends that changes linearly over a certain range on both sides of the central position with a parallel displacement (direction x), where When passing through the center position, the phase position is rotated by 180 ° with respect to the transmission signal.
In this way, a simple sensor can be realized, which can be used to measure the parallel displacement of the two coils relative to each other, and the resulting measurement path is somewhat larger than the coil diameter of the transmitting coil. small.
As already explained, the induced reception voltage is linear in the central region and gradually increases in non-linearity towards the edge of the region.
At this time, the characteristic of the gradient on the measurement path depends on the basic distance of the coil.

FIG. 4 shows a combination of the assemblies of FIGS.
Two receiving coils (2) and (3) are nested in each other.
The coil surface of the receiving coil (3) is located on the axis of the receiving coil (2).
Since the gradient characteristic of the reception voltage (E3) does not depend on the distance to the rectangular coil (1), the electromagnetic field strength must be measured using the second reception coil (2) (reception voltage E2).
By forming the ratio of the two received voltages (E3 / E2), the distance independence of the position measurement in the z direction is realized over a certain displacement range.
At this time, it should be noted that the sign is reversed when passing through zero due to the phase rotation caused by the dominant electromagnetic field direction.

FIG. 5 shows another possibility of placement, ie the use of two transmit coils (1a) and (1b), which are placed next to each other on the same plane (1ab).
The two receiving coils (2) and (3) are also located adjacent to each other at the same distance and are mechanically firmly connected.
A constant AC voltage (S) is simultaneously supplied to the transmission coil.
As in the case of FIG. 4, it also applies here that the distance-independence of the position measurement in the z direction is achieved by the ratio formation (E3 / E2).

  Similarly, a combination of coil (4) and receiver coil (2) is possible and considered an invention.

  FIG. 6 shows another embodiment of the present invention that extends to three measurement axes.

In order to minimize the required number of transmit coils, there is the possibility of placing the two receive coils (5) and (6) very close to each other.
This can be done for either the x direction or the z direction.
If the two coils are arranged so that their common axis extends in the x direction as shown in FIG. 6, the following applies:

That is, from the sum of the resulting two received voltages (E5) and (E6) to the distance to the transmitter coil (1a) and thus to the plane (1ab) where the two transmitter coils (1a) and (1b) are located A signal related to the distance is obtained.
The difference between the two voltages (E5-E6) gives the position with respect to the center of the transmitting coil (1) in the x direction.
Therefore, also in this case, due to the ratio formation ((E5−E6) / (E5 + E6)), the measurement of the position in the x direction does not depend on the distance between the two coils with respect to the plane (1ab).
At the same time, a distance-independent measurement for the position in the z direction can be similarly determined using the ratio (E3 / (E5 + E6)).
All of these assemblies require that the transmit coil be connected to an AC power source via a cable.

FIG. 7 shows another embodiment of the present invention, i.e. another possibility of eliminating the need for cabling.
An additional coil (1c) that functions as a receiving coil for power feeding is arranged on the same plane as the transmitting coil.
A transmitting coil (7) mechanically connected to the receiving coils (3), (5) and (6) is located facing the coil (1c).
By supplying a constant AC voltage (SS), a constant electromagnetic field is radiated by the transmitting coil (7).
At this time, the voltage induced in the coil (1c) is supplied to the two transmission coils (1a) and (1b) by direct electrical connection.

According to the description of FIG. 8, in the context of a further embodiment of the invention, for example, an angle-dependent measurement error (angle) that occurs during the assembly of two sensor units A (receiver coil) and B (transmitter coil). α) can be compensated.
For this purpose, a further receiving coil 8 may be positioned in the center between the two receiving coils 5, 6.
Again, the sum of the received voltages E5, E6 gives a measured distance in the y direction, for example to allow an accurate alignment of the two sensor units A, B with respect to each other during assembly, and the angle α The dependent reception voltage E8 and the differential voltage (E5-E6) can be simultaneously measured and set to zero by mechanical adjustment.
Therefore, very accurate calibration is possible.

Further, the differential voltage (E5-E6) caused by the presence of some angle error remains constant with respect to the displacement of the two sensor units A and B in the x direction.
As a result, errors can be eliminated by computation instead of eliminating errors by mechanical alignment.
In this case, the angle error k generated in the received voltage E8 at the same rate as the difference voltage (E5-E6) as a function of the angle α is multiplied by the matching coefficient m and subtracted from the signal E8.

  The displacement in the x direction in this case is measured using the voltage ratio (E8−k × m) / (E5 + E6).

In order to optimize the sensitivity of all these assemblies, it is beneficial to connect capacitors in parallel so as to complete the coil to an oscillating circuit whose resonance is adjusted to the operating frequency.
This reduces the supply current required on the transmit side of the transmit coil, and at a close distance to the transmit coil, the receive voltage (inductance of the receive coil is only slightly smaller or greater than the transmit voltage). Is given to the receiver).
Therefore, a very good signal to noise ratio is obtained.

Of course, these assemblies represent examples only.
In principle, other assemblies of this type are conceivable.

1, 1a, 1b Transmission coil 2 Reception coil 3 Reception coil 4 Reception coil 5 Reception coil 6 Reception coil 8 Reception coil 1ab Planar S AC voltage E2 Reception voltage E3 Reception voltage E4 Reception voltage E5 Reception voltage E6 Reception voltage E8 Reception voltage

Claims (10)

It has at least two coils: a first coil that is supplied with a specific frequency so as to emit a constant electromagnetic field, and a second coil that receives or detects the electromagnetic field, and the axis of the second coil is An angle is formed with respect to the axis of the first coil, the first coil is disposed on a first object, the second coil is disposed on a second object, and the first object and the second object A position sensor for measuring the relative position between
The position sensor further includes a fourth coil that radiates a constant electromagnetic field, and a fifth coil and a sixth coil that receive or detect the electromagnetic field of the fourth coil, and the first coil includes the first coil Mechanically connected to the fourth coil, the axis of the fourth coil is positioned in the same direction as the axis of the first coil, and the first coil and the fourth coil are adjacent to each other Arranged, the second coil is arranged adjacent to the fifth coil and the sixth coil, and the fifth coil and the sixth coil are arranged very close to each other, ie , Position sensors that are arranged adjacent to each other in the x direction or adjacent to each other in the z direction and whose common axes extend in the same direction.   The position sensor according to claim 1, wherein an axis of the second coil forms an angle of 90 ° with respect to an axis of the first coil.   The position sensor according to claim 1, wherein the first coil is formed as a rectangular coil.   The position sensor according to claim 1, wherein the second coil is formed as a rectangular coil.   Further comprising a seventh coil for receiving or detecting an electromagnetic field of the fourth coil, wherein the fifth coil, the sixth coil, and the seventh coil are disposed in close proximity to each other; That is, the position sensor according to claim 1, which is disposed adjacent to each other in the x direction or adjacent to each other in the z direction, and their common axes extend in the same direction.   The position sensor according to claim 1, wherein an additional coil that functions as a power receiving coil is disposed on the same plane as the first coil and the fourth coil.   A transmission coil mechanically firmly connected to the second coil, the fifth coil, and the sixth coil is disposed with respect to the additional coil, and supplies a constant AC voltage. The constant electromagnetic field is radiated through the transmitter coil, and the voltage induced in the additional coil is delivered to the first coil and the fourth coil by direct electrical connection. Position sensor. The first coil and the fourth coil are arranged next to each other on the same plane;
8. The postures of the first coil and the fourth coil are perpendicular to at least one of the second coil, the fifth coil, and the sixth coil. The position sensor described in 1.   The position sensor according to claim 5, wherein the first coil, the second coil, and the fourth to seventh coils are completed in an oscillation circuit. The position sensor according to claim 5, wherein the first coil, the second coil, and the fourth to seventh coils are formed on a plurality of ceramic layers or in a plurality of ceramic layers.

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